In the prior art, many cards such as identification certificates, driving licenses, membership cards, etc. have been used, and on these cards is recorded various information for clarifying identification, and the like, of the owner. Particularly, on ID cards, and the like, a face photograph is the most important feature.
A classical method for imparting face photographs on to various cards is a method of securing a face photograph to a predetermined portion of a card substrate by use of an adhesive, but this method is very cumbersome in its operation, and also has the drawback that unevenness is created on the card surface.
Whereas, in the prior art, there has been developed an image forming method according to the sublimation transfer method. The sublimation transfer method is a method in which a sublimation transfer sheet, having a layer containing a dye which is sublimation transferred by heat on the surface of a substrate film and an image receiving sheet are superposed, and a desired image is formed on the image receiving sheet by heating with a thermal head according to an image information from the back of the sublimation transfer sheet, and there is the advantage that it can be practiced by a simple heat transfer printer.
Whereas, when the sublimation transfer system is applied to a card medium such as an ID card, the card substrate is demanded to have sufficient dyeability for a sublimable dye. However, most of the card substrates of the prior art have no sufficient dyeability for sublimable dyes, and therefore no image formation can be effected thereon as such. As the method for solving such drawback, a method of previously forming an image receiving layer excellent in dyeability for a sublimable dye may be conceivable, but formation of such image receiving layer on a card substrate is cumbersome in steps, whereby there is the problem of increasing the production cost of the card substrate. Further, when an image receiving layer is provided separately on the surface of a card substrate, there will ensue such problems that the card substrate may be curled or the image receiving layer may be peeled off as caused by the heat applied during image formation.